Field of the Invention
This invention relates to a bicycle and more particularly, to an inner air-tube of the tire for a bicycle, particularly a racing bicycle.
As is well known, the tire tube for the racing cycle is required to have high strengths and light weight so as to stand use under conditions of high pressure and high speed. Whether the above requirement is satisfied or not is greatly influenced by the performance of the inner air-tube of the tire. Accordingly, much care is paid to selection of materials for the inner tube of the cycle tire and very high processing techniques are needed for making of such tube.
Several types of the inner tube of the tire are known including those made from latice of natural rubber, those obtained by extruding and vulcanizing natural rubber or butyl rubber, and the like. However, those known tubes have all advantages and disadvantages and are not necessarily satisfactory in practice. For instance, the tubes obtained from the rubber latice or by extrusion and vulcanization of natural rubber are great in tensile strength, elongation and resistances to tear and puncture and also in repulsion elasticity, thus showing good running performance, but are disadvantageously low in retentivity of air and resistance to aging. On the other hand, the extruded and vulcanized tubes of butyl rubber show excellent air retentivity and aging resistances to puncture and burst but are smaller in tensile strength, tear resistance and resistances to puncture and burst. In addition, they exhibit poor repulsion elasticity and a poor resistance to abrasion, thus impeding the running performance. The physical strengths of these two types of the tubes are summarized in Table 1 below as determined according to the methods prescribed in Japanese Industrial Standards.
TABLE 1 ______________________________________ Tube from Extruded and Natural Vulcanized Tube Rubber Latex of Butyl Rubber ______________________________________ tensile strength 300 130 (kg/cm.sup.2) elongation (%) 700 650 tear strength (kg/cm) 40 30 repulsion elasticity 70-80 40-50 air retentivity* 1 7.5 ______________________________________ Note *The air retentivity is expressed in terms of an index when the latex tub is taken as 1.